1. Field of the Invention
The invention relates to a pump mechanism which is to be attached to a container filled with a liquid such as hand soap, a shampoo, or a hair rinse and which sucks up the liquid from the container and then ejects the sucked liquid.
2. Description of Related Art
Recently, because of ease of use, a liquid supplying device which is configured so as to supply a suitable amount of a liquid by a one-push operation is widely used. In such a device, particularly high importance is placed on a pump mechanism which sucks up the liquid stored in the container and ejects a constant amount of the liquid.
Referring to FIGS. 9 and 10, the structure of a prior art pump mechanism will be described. FIG. 9 is a half section view of the pump mechanism in a state before the liquid ejection, and FIG. 10 is a half section view of the pump mechanism in a state after the liquid ejection.
In FIGS. 9 and 10, a cap-shaped base portion 31 is screwed to an opening of a container (not shown) which is filled with a liquid. A cylinder 32 is fixed to the base portion 31. A ball valve 33 is disposed at the lower end of the cylinder 32. A tube (not shown) for sucking up the liquid via the ball valve 33 is connected to the cylinder 32. A hollow shaft 34 has a cup-shaped piston 34a at its lower end. The outer peripheral face of the piston 34a is closely contacted with the inner peripheral face of the cylinder 32.
A head 35 and a nozzle 36 which are integrated with each other are attached to the upper end of the shaft 34. A ball valve 37 is disposed at a position of the shaft 34 in the vicinity of the head 35.
A coil spring 38 which is made of a metal is placed between the cylinder 32 and the shaft 34. A guide member 39 is disposed so that the coil spring 38 does not deflect into an L-like shape but vertically expands and contracts. The guide member 39 functions also as a stopper which restricts the movable range of the ball constituting the ball valve 33.
In the thus configured pump mechanism, when the head 35 is pushed down under the state where the liquid stays in the cylinder 32 (the state shown in FIG. 9), the liquid pressure is raised and only the ball valve 37 is opened so that the liquid is ejected through the nozzle 36.
When the head 35 is released under the state where the ejection of the liquid is completed (the state shown in FIG. 10), the piston 34a is pushed up by the recovery force of the coil spring 38 which has been compressed during the operation of pushing down the head 35. At this time, a negative pressure is generated in the cylinder 32 and only the ball valve 33 is opened so that the liquid is sucked up into the cylinder 32 and the ejection preparatory state is established.
When such a prior art pump mechanism is to be subjected to a disposal process or a recycle process, materials of different kinds, i.e., resins and metals must be separated from each other prior to the execution of such a process. Specifically, a pump mechanism is manually once disassembled, and the coil spring 38 made of a metal is then detached from the body made of a resin. Therefore, the disposal cost is high.
In the pump mechanism, when it is used for a long period, there is the fear of a trouble due to the reduction of the performance of the coil spring 38. Specifically, the coil spring 38 is always immersed in the liquid and hence easily rusts. This may cause the resilient force to be reduced or the spring to be broken. When such a defect occurs, the coil spring 38 cannot exert a required resilient performance and hence the positional recovery of the piston 34a is disabled. As a result, the liquid cannot be again ejected.
A prior art pump mechanism has a further problem in addition to the problems discussed above. Namely, in order to reduce the consumption of raw materials in production and efficiently use resources, it is strongly requested to reduce the size of a pump mechanism and simplify the structure of the pump mechanism.
The pump mechanism has a further problem as follows: The degree of the recovery force of the piston 34a must be appropriately set in accordance with the kind of the liquid. When a gel liquid having a high viscosity is to be handled, for example, the recovery force must be set to be high. This is because a liquid having a high viscosity is inferior in flowability and the piston 34a must be raised at a higher speed so that a negative pressure higher than that in the case of a usual liquid is generated in the cylinder 32. To comply with this, in the prior art, the recovery force is adjusted by replacing the coil spring 38 with one having another resilient force, i.e., another spring constant. Consequently, it is required to prepare various kinds of coil springs having different spring constants so as to increase the production cost.